The United Nations Navy (abbreviated UNN) is the naval force of Earth and the United Nations. It is considered less technologically advanced than its Martian counterpart, the Martian Congressional Republic Navy, but has the largest fleet in Sol system.
- The Agatha King - Truman Class Dreadnought.
- The Okimbo - Truman Class Dreadnought.
- The Thomas Prince - Xerxes Class Battleship.
- The Seung Un - Destroyer.
- The Arboghast- Destroyer.
- The Ravi - Corvette.
- The Wu Tsao - Frigate
- The Dagmar - Unknown Class.
- The Macedon - Unknown Class.
- The Munroe - Munroe Class Destroyer
- The Darius - Unknown Class
- The Greenville - Unknown Class
- The Tanaka - Unknown Class
- The Dyson - Unknown Class
- The Kennedy - Unknown Class
- The Triton - Unknown Class
- The Nathan Hale - Transport/Destroyer
When the Donnager is destroyed by what is believed to be OPA ships, and Mars declares war on the Belt, the the UN stays neutral. Later when Holden released information on the ships that destroyed the Donnager were actually made on Earth, UNN ships fired on Martian Congressional Republic Navy ships in Mars' orbit and destroyed the Deimos deep radar station. After securing Martian space, the UNN begin laying siege to Mars, forcing, the MCRN then orders nearly all their ships in the system to return to Mars and declares war on Earth. The Belt claims it a victory, and the siege lasts for months. However, all combat remains in orbit and doesn't spread onto Martian soil.
The Charles Lyell, a science vessel, escorted by the Ravi, was doing a non-Belt asteroid mapping when it was diverted to Eros to collect samples of the Protomolecule. It was in a confrontation with the Rocinante until they finally worked together to stop the asteroid.
The Ganymede incident was an event where a human-protomolecule hybrid attacked Martian and UN Marines on Ganymede, killing everyone except Gunnery Sergeant Roberta Draper. The initial attack was misinterpreted by both the MCR and the UN as an attack from the other side, which lead to a battle above and on Ganymede that claimed nearly three thousand military and civilian lives, as well as over five billion MCR dollars of infrastructure damage.